Electrode gas removal method and apparatus



May 23, 1933. F. MEYER Er AL 1,910,557

ELECTRODE GAS REMOVAL METHOD AND APPARATUS Filed Dec. 29, 1927 BYf Ma gaf/muv? ATTOR Patented May 23, 1933 PATENT OFFICE.

FRIEDRCI-I MEYER AND HANS JOAGHM SPANNER, OF- BERLIN, GERMANY, AND

EDIEUND GERS/2ER, OF STOCEIH'LM, SWEDEN, ASSIGNORS, BY MESNE ASSGNMENT' TO ELECTRGNS, NC., A CORPORATON OF DELAWARE ELEGTRODE GAS REMOVAL METHOD AND APPARATUS Application filed December 29, 1927, Serial No.. 243,291, and in Germany January 10, 1927.

This invention relates to the removal of gases occluded in electrode materials commonly used in thermionic and like vacuum tubes, particularly desirable in those tubes employing high vacuum.

lt is well known that in order to obtain a high vacuum in vacuum tubes'that will remain permanent it is necessary to free the materials of which the electrodes are made of their occluded gases during the vacuum pumping process and before the tubes are sealed, and this must be done irrespective of the character of the material, usually metal, ojf which the electrodes are composed.

rlfhis electrode gas removal has always been one oit the exacting difficulties in the manufacture oi. thermionic and like discharge tubes where the tube is intended to be so employed that its vacuum should be permanently maintained at the highest possible value.

Various methods have been devised for carrying out this electrode cle-gasing and the art has succeeded in producing tubes capable of maintaining in use a very high vacuum. However, methods heretofore employed are complicated and expensive, or else aiiect the physical and electrical characteristics oit the electrodes, especially coated cathodes, to an undesired extent with the result that these vital parts of the tube initially suifer from the de-gasing process.

According to the present invention, it is possible to obtain a high degree of de-gasing ot the electrodes in vacuum tubes without any of the disadvantages and ill effects of previous methods. rlhe present method principally consists in introducing` into the tube or container, which has iirst been evacuated to a desired degree with the customary pumping` means, a small quantity of a non-absorbable gas, in particular an inert gas, examples of which gases are argon, neon, crypton and helium, and producing in the presence of this introduced gas an electric discharge between the several electrodes with the aid of suitable electrical potentials applied to the electrodes under treatment. Vith the proper selection of the gas pressure and the potentials an ionic bombardment of the electrodes under treatment will produce sufficient heat in them, such as a iull glow, to cause them to easily expel their occluded gases into the surrounding atmosphere of inert gas. During the discharge, or subsequent to its interruption, the gas mixture thus produced is withdrawn from the container with the aid of the vacuum pump. Usually it is suticient to till the container but once with the inert gas, but if particularly high degrees of permanent vacuum are being sought-the operation may be repeated one or more times.

The method is economical from the point of view of' inert gas consumption since satisfactory discharge vconditions can be obtained with a pressure of inert gas of the order of l millimeter. The pumping and electrical apparatus required is very simple and of a kind readily available in organizations making tubes.

The method is of particular advantage in the kmanufacture of thermionic tubes, such as transmitting and receiving tubes for radio. One effective way of de-gasing. such tubes consists in bombarding the electrodes with the aid of the electron emission ytrom the heated filament or cathode. This procedure, however, involves the objection that the ions present during the continuance of the discharge bombard the filament or cathode quite violently, with the result that'it suffers some destruction which at least shortens its useful lite and which, in the case of highly active or emissive cathodes, decreases their emissive quality.

To avoid the destructive effect-of ionicv bombardment of the more or less fragile cathodes, simple expedients may be resorted to. Thus the bombarding discharge may be produced between electrodes which are not cathodes, and the necessarily present cathode be protected from theionic movement through the aid of ion repelling potentials applied thereto; or, the cathode may be heated in thc normal way to create thereabout a cloud or ield of electrons whose negative charge willsuiiciently neutralize the -positive ions attemptingto approach the cathode. Again, the cathode may be protected by applying a protecting potential to another properly located electrode, for instance, the grid, when the bombarding discharge is produced between other electrodes. lr" sutlicient electrodes are not available in the construction of the tube, one or more auxiliary electrodes may be deliberately inserted therein for the purpose of facilitating the process, though such auxiliary electrode may not thereafter be needed in the ordinary functioning of the tube.

lf the electrodes are oi' more or less widely diiierent dimensions, or otherwise constituted so that one contains a considerable quantity of occluded undesirable gas and the other contains little of' such gas, it is suilicient to use the electrode containing` the greater quantity of gas as the cathode in the bombarding process', but such procedure is necessarily limited to direct current boinbardment; in other words, it is a one-way process. lf there are two electrodes each containing large amounts of gas, as by having large masses, a complete de-gasrng of these electrodes can be obtained by commutating or periodically reversing the potential applied to them from a direct current source, oran ordinary alternating current source may be depended upon.

lt is of course understood that tubes degased by the procedure outlined in this invention may receive a final clean-up treatment according to any of the well known clean-up processes employing so-called getter materials.

rlChe method and apparatus employed will be further understood by reference to the figures of the accompanying drawing in which like reference characters represent like Vparts so tar as possible throughout the several figures.

Fig. 1 shows the method applied to an ordinary three-electrode vacuum tube.

Fig. 2 shows the method applied to an ordinary three-electrode vacuum tube in which an auxiliary anode is introduced.

Fig. 3 shows the method employed in a three-electrode tube having two grids.

Fig. el shows the method employed in connection with an ordinary two-electrode tube having two anodes for so-called full-wave7 rectilication.

lteierring to Fig. l, VT is the ordinary glass or like container for a vacuum tube shown alternately connectable to a vacuum pump and a source ot inert gas by means ot the two-way cock V through the communicating stem K. The tube is shown to include, in well known form of construction and support on a stem S, a filament F, a grid G and a plate P. A potential is shown applied between the grid G and the plate P from a source B1, which may be a battery or other suitable source of' potential, the magnitude of potential being controllable through the variable resistance R. The negative side of the source is shown connected to the plate P so that in this case the plate acts as a cathode, which is in accordance with the previous comments as to a procedure when one electrode, such as a plate of large mass, is being worked with another electrode, such as a grid, with small mass. Battery B2, or like source of potential is shown connected between the grid G and the lilament F, the negative side of the source being connected to the filament, thus to apply a negative potential to the filament with respect to the grid to protect it from ionic bombardment as previously discussed. The potential can be readily applied or removed by means of the switch N. With the arrangement shown the tube VT can be pumped to a hiOh degree by proper adjustment 01"' the cock V, after which the desired amount of inert gas is permitted to enter through movement of the same cock. The potential of B1 is then applied to create the desired discharge, which discharge is regulated in intensity by the resistance R. When the electrodes under treatment have reached the necessary temperature for the particular material to eXpel the occluded gases, which condition is generally indicated by a full red glow, the discharge may be interrupted and the vacuum pump then applied to remove the resulting mixture ot gases. During the process the switch N may be closed to apply the protecting potential to the ilament. lt the operation is not to be repeated the tube is then sealed oit at the base of the communicating stem K when the vacuum pump has produced the desired degree oi? vacuum. The final clean-up by the getter process may be completed before the sealing off or after, depending upon the particular clean-up process employed.

Fig.2 differs from Fig. l in that an auxiliary electrode A is included in the electrode structure of the tube, and a source of potential Sl is shown connected between this auxiliary electrode and/or the grid, the two being shown cross-connected in the ligure. ln this case the discharge between these two electrodes may be obtained by means of an alternating current, or a commutated or periodically reversed direct current, so that the electrodes alternately act as cathodes, this procedure being previously discussed, The ligure also shows the secondary winding S2 of an alternating current transformer connected across the terminals of the filament F to heat this filament to produce a cloud of electrons thereabout as a protection against ionic bombardment.

The details of the vacuum pump and inert gas connection are omitted in Fig. 2 and the succeeding figures for brevity, it being understood that they are the same as in Fig. l, or equivalent connections.

Fig. 3 differs from Fig. 1 in that an electrode structure is shown which includes two grids,` one being shown inside ot the other. In this arrangement the connections for producing the discharge are made between the plate P and the outer grid G1. There are shown means for applying a potential to the inner gride G2 that is positive to the outer grid G1, which potential acts to protect the cathode passing through the inner grid from ionic bombardment.

Fig. 4L shows a form of tube commonly employed for rectiiying alternating currents, the two plates P1 and P2 cooperating with the single ilament F to produce what is commonly termed full-wave rectiiication. The arrangement shows means for connecting a potential S1 between the two plates P1 and P2 to produce a discharge therebetween that alternately requires each of the two plates to serve as cathodes. Of course, direct current may be used wherein one plate is bombarded for a time and the operation then shifted so that the other plate is bombarded for a time, and this is also true of all of the gures where alternating curient sources of potential have been indicated. There is also shown the secondary winding S2 of a transformer connected across the terminals of filament F, or filaments if there be more than one, for heating the same to produce a cloud or ield of electrons thereabout for protection against ionic bombardment. OI" course, direct current may be used for heating the ilament in this and the other figures of the drawing.

Vhile we have shown and described specific arrangements for employing our invention, we do not desire to be limited by the particular arrangements chosen merely for illustrative purposes, and our invention is of the scope set :forth in the annexed claims.

Having thus fully described our invention, we claim:

1. In the practice of fabricating thermionic and like discharge tubes, the method of cle-gasing the included electrodes 'in the presence of an electrode subject to injury by ionic bombardment which consists of evacuating the tube, admitting a quantity of inert gas, producing an ionic discharge with the aid of said gas and applied potential between chosen electrodes other than the electrode subject to injury sufficient to produce by bombardment a gas expelling temperature in said electrodes, shielding said electrode subject to injury during said discharge by maintaining around said electrode an electric charge positive to that of said electrode, and further evacuating the tube of the resulting gas mixture.

2. In the process of de-gasing electrodes by ionic bombardment, the method of protecting a present electrode subject to injury by such bombardment which consists in permits taining=saidgridat a potential more posicausingthe bombardmenttotake place inan atmosphere `oiiiiert gas 'ata pressurewhich a low Vvoltage .ionico discharge between `the electrodes tobe degassed and so charging the electrode to be yprotected dur-2v yingy the. bombardment process .that vthe ions .fare diverted therefrom.

'3.3.' Inthe process .of de-gasing `electrodes "byionic bombardment'in the presence of an electrodesubject to injury by such bombard-f ment, the. method ofA y'protecting said 'elecvtrode .from .destructive bombardment kwhich -consistsv oi iinterposingi between said. .electrode andf lthe region of ionic.l activity` an electrode :soa electrically charged'i withf respecti'toirsaid' protected Ielectrode: that the ions'` are prevented from substantive; bom- `-bardment ofsaid protected electrode.

- 4. In the process of fabrication of vacuum tubes having an anode, grid, and cathode,''f kthe steps of evacuatingthe envelopeY oi said tube, introducing asmalliquantity of inert Igas therein, producing a potential gradient betweenv said cathode andvsaid anode, and maintaining ysaid .grid at a potential moref lpositiveithan .either saidv anode or said=cath ode, whereby -said cathode is substantially -protected from ionic bombardment.

5.' In lthe process offabrication 'of vacuum tubes having an anode, a grid andalcathode, *Y thesteps of evacuating'the envelope 'of said tube, introducing therein a ksmall quantity 'of inert gas, producing a potential gradient between said cathode and said anode, maintive than' either. said` anodefor said cathode, whereby the anode is subjected to. a'greater degree of'boinbardment than said cathode, andfevacuating themixture of vthe inert gas and the gases expelled fromsaid electrodes"4 and refilling said envelope with inert gas to the desired pressure.

6. In the process of fabrication of vacuum tubes having an anode, a grid, and a cathcold electrode in the presence of an oxideff120 coated cathode which consists in applying voltage between said electrode and another cold electrode, other than the oxide coated cathode, to cause the said electrode, to act as a cathode and be subjected to ionic bom-5125 bardment, causing the bombardment to take place in an atmosphere of inert gas at a pressure which permits a low voltage ionic discharge, and protecting the oxide coated,130

cathode from bombardment by maintaining ode, the steps of evacuating the envelope22110 an ion repelling means in proximity thereto.

8. The process of degassing a normally cold electrode in the presence of an oxide coated cathode which consists in applying voltage between said electrode and another cold electrode, other than the oxide coated cathode, to cause the said electrode to act as a cathode and be subjected to ionic bom-` bardment, causing the bombardment to take place in an atmosphere of inert gas at approximately one mm. of pressure, and protecting the oxide coated cathode fromionic bombardment by maintaining an ion repelling charge in proximity thereto.

9. ln combination a discharge tube containing an inert gaseous medium at approximately l mm. of HS pressure, an oxide coated electrode and two cold electrodes, connections between said cold electrodes and a voltage source adapted to cause a luminous discharge in said inert medium across said cold electrodes, and connections to said oxide .coated electrode adapted to create a charge thereabout which is repellent to ions from said luminous discharge.

10. The method for cle-gassing a discharge tube having three electrodes which are normally cathode, anode and grid, respectively, which comprises the steps of evacuating the tube, filling the tube with inert gas at a predetermined pressure, and applying potentials to said electrodes with the grid suwiciently positive relative to the anode tocause an ionic discharge between the grid and anode, and with the cathode charged relative to the grid to prevent substantial bombardment of said cathode.

FRlEDRlCl-l MEYER. HANS JOAGHM SPANNER. EDMUN D GERMER. 

